With respect to vehicle tires, the two major ingredients in a rubber compound are the rubber itself and a filler, combined in such a way as to achieve different objectives. Depending on the intended use of the tire, the objective may be to optimize performance, to maximize traction in both wet and dry conditions, or to achieve superior rolling resistance. The desired objective can be achieved through careful selection of one or more types of rubber, together with the type and amount of filler to blend with the rubber.
In general, there are four major rubbers used: natural rubber, styrene-butadiene rubber (SBR), polybutadiene rubber (BR), and butyl rubber (along with halogenated butyl rubber). The first three are primarily used as tread and sidewall compounds, while butyl rubber and halogenated butyl rubber are primarily used for the inner liner, which is the inside portion that holds the compressed air inside the tire.
The most popular fillers are carbon black and silica, and there are several types of each. Recycled rubber powder can also be used as part of the formulation. The selection depends on the performance requirements, because they are different for the tread, sidewall, and apex. Other ingredients also come into play to aid in the processing of the tire or to function as anti-oxidants, anti-ozonants, and anti-aging agents. In addition, the “cure package”—a combination of curatives and accelerators—is used to form the tire and provide its elasticity.
Once the formulation is determined, the next challenge is how to mix all of the ingredients together. The mixing operation is typically a batch operation, with each batch producing more than 200 kg of rubber compound in fewer than three to five minutes. The mixer is a sophisticated piece of heavy equipment with a mixing chamber that has rotors inside. The main function of the mixer is to break down the rubber bale, fillers, and chemicals and mix them with other ingredients.
The sequence in which the ingredients are added can be critical, as well as the mixing temperature, which can rise as high as 160° C. to 170° C. If the temperature is too high, the compound can be damaged, so the mixing operation is typically accomplished in two stages. The curative package is normally added in the final stage of mixing, and the final mixing temperature cannot exceed 100° C. to 110° C. to prevent occurrence of scorching.
Once the mixing is completed, the batch is dumped out of the mixer and sent through a series of machines to form a continuous sheet called a “slap.” The slap is then transferred to other areas for bead wire assembly preparation, inner liner calendering, one or both of steel and fabric belt/ply cord calendering, tire sidewall extrusion, and tire tread extrusion.
Tire components such as tread, sidewall, and apex are prepared by forcing uncured rubber compound through an extruder to shape the tire tread or sidewall profiles. Extrusion is an important operation in the tire manufacturing process because it processes most of the rubber compounds produced from the mixing operation and then prepares various components for the ultimate tire building operation.
With respect to battery separators, a lead-acid storage battery is commonly found in two modes of design: the valve-regulated recombinant cell and the flooded cell. Both modes include positive and negative electrodes that are separated from each other by a porous battery separator. The porous separator prevents the electrodes from coming into physical contact and provides space for an electrolyte to reside. Such separators are formed of materials that are resistant to the sulfuric acid electrolyte and sufficiently porous to permit the electrolyte to reside in the pores of the separator material, thereby permitting ionic current flow with low resistance between adjacent positive and negative plates.
Separators for lead-acid storage batteries have been formed of different materials as the technology has developed. Sheets of wood, paper, rubber, PVC, fiberglass, and silica-filled polyethylene have all found use over time. A type of separator currently favored for use in flooded lead-acid storage batteries used in automotive starting-lighting-ignition (SLI) service is the silica-filled polyethylene separator. The microporous polyethylene matrix contains a large fraction of silica particles to provide wettability for the acid electrolyte and to help define the pore structure of the separator. A separator of this type is described in U.S. Pat. No. 7,211,322.
Another application for flooded lead-acid storage batteries is the traction or deep-cycle battery, which commonly uses a separator made partly of rubber. Traditionally, this separator was a porous hard rubber, cross-linked with sulfur. Improvements on the rubber separator have included the addition of silica particulate filler to the rubber matrix before curing, and cross-linking with electron-beam radiation instead of chemical cross-linking agents.
All of these rubber-containing separators have the advantageous effects for deep-cycle batteries of promoting long cycle life by controlling water loss during charge. During the charging of the lead-acid storage battery, the active material on the negative electrode is first reduced from lead sulfate to lead. As the available active material is converted to lead, the potential of the electrode is lowered. As the potential on the negative electrode drops, an increasing fraction of the charging current is involved in the evolution of hydrogen by reduction of the hydronium ions present in the adjacent electrolyte. Meanwhile, at the positive electrode, the charging operation is oxidizing the active material from lead sulfate to lead oxide, accompanied by a rise in the potential of the positive electrode. As the potential rises, an increasing fraction of the charging current is involved in the production of oxygen by oxidation of adjacent water molecules and the production of hydronium ions to replace those consumed at the negative electrode. The net effect of the evolution of hydrogen at the negative electrode and the evolution of oxygen at the positive electrode is the consumption of water from the acid electrolyte. This loss of water results in an increase in the concentration of the sulfuric acid, an increase in the resistance of the battery, and eventual failure. By reducing the rate of water loss from the battery, rubber-containing separators extend the service life of deep cycle batteries.
Despite the advances made in the art with respect to improved separators containing some form of rubber, there continues to be a need for a low-cost separator, with low resistance to ion flow that limits the water loss and improves the cycle life of lead-acid storage batteries used in deep cycle service.